Hyperacute rejection mediated by immune allogeneic sera and normal xenogeneic sera will be studied in an in vitro model of heart perfusion through coronary vessels, in order to assess the role of antibodies and complement in this rejection. Soluble antigenic tissue preparations will be tested for their activity in neutralizing antibodies in xenogeneic sera using the heart perfusion model. Selected tissue preparations will be used to neutralize in vivo antibodies of a recipient of xenogeneic cardiac graft. Prolongation of graft survival to several days is anticipated. Glomerular lesion responsible for late deterioration of renal allografts will be studied in order to assess the role of circulating complexes of transplantation antigens and antibodies in formation of this lesion. Studies on cell membrane antigens will be performed on interspecies hybrid cells wth the aim of isolating individual species antigens of the cell surface and initiating studies on genetic repair of enzymatically deficient cells. Skin-reactive transplantation antibodies, which are homocytotropic antibodies of rat, will be investigated for their biological role such as graft rejection or enhancement. Effect of presensitization of females to the histocompatibility antigen of their future mates on fetal and neonatal mortality will be investigated with the specific aim of identifying antibodies that are presumably responsible for placental damage.